An electrostatic printing system and method in which a charged particle stream directed toward a print receiving medium is selectively controlled by mechanical and electrical modulation or shuttering and mechanical motion of the shutter area to achieve character serial and line serial printing....http://www.google.com/patents/US3815145?utm_source=gb-gplus-sharePatent US3815145 - Electrostatic printing system and method using a moving shutter area for selective mechanical and electrical control of charged particles

Electrostatic printing system and method using a moving shutter area for selective mechanical and electrical control of charged particlesUS 3815145 A

Abstract

An electrostatic printing system and method in which a charged particle stream directed toward a print receiving medium is selectively controlled by mechanical and electrical modulation or shuttering and mechanical motion of the shutter area to achieve character serial and line serial printing.

I 1 ELECTROSTATIC PRINTING SYSTEM AND METHOD USING A MOVING SHUTTER AREA FOR SELECTIVE MECHANICAL AND ELECTRICAL CONTROL OF CHARGED PARTICLES [75] Inventors: Thomas A. Tisch, Saratoga; Thomas A. Jenkins, Redwood. both of Calif.

PATENTEDJun 4 I974 SHEET 5 0f 6 FiG 9 ELECTROSTATIC PRINTING SYSTEM AND METHOD USING A MOVING SHUTTER AREA FOR SELECTWE MECHANICAL AND ELECTRICAL CONTROL OF CHARGED PARTHCLES The present invention generally contemplates pro-- viding a line source of ions for generating an ion stream in the direction of a print-receiving medium which is supported and transported relative to the ion stream. A printing head is interposed between the ion source and print-receiving medium which generally blocks the ion stream. The printing head is formed with at least one shutter area comprising a plurality of electrically addressable apertures for electrostatically controlling the flow of ions through the apertures in accordance with electrical signals applied to the apertures. Thus, while the ion stream is generally mechanically blocked by the printing head, ions are selectively passed through the apertures of the shutter area to form on the printreceiving medium, for example, an electrostatic latent dot matrix which is thereafter developed according to known techniques to provide alphanumeric characters, images or other symbols. By motion of the printing head the shutter area or shutter areas are transposed in a direction across the print-receiving medium for selective exposure of ions in accordance with electrical signals applied to the apertures at sequential positions across the print-receiving medium. By this expedient, rows of electrostatic latent dot matrices are formed sequentially across the print-receiving medium for development into, for example, alphanumeric characters, images and other symbols.

A feature and advantage of the system arrangement using both selective electrical modulation of the ion stream in a shutter area, mechanical blocking outside the shutter area, and mechanical motion of the shutter area is that character sequential or character serial and line-by-line printing of hard copy alphanumeric output from conventionally coded electrical signals is achieved for application in data processing and data transmission systems. Moreover, the character serial and line serial printing format of the present invention is inherently compatible with such applications, thereby eliminating the need for extensive data buffering, affords high printing rates, and permits significant reduction in the complexity of the printer over conventional devices with consequent lower costs.

According to one aspect, the invention contemplates effective helical scanning of a shutter area across a print-receiving medium. In one embodiment, the printing head which generally blocks the ion stream, supports a shutter area for selectively exposing the printreceiving medium, and scans the shutter area in a direction across the print-receiving medium comprises a tube or annular cylinder of solid material surrounding a line source of ions such as a corona wire. A plurality of aperture groups, each forming a shutter area, are arranged in a helix around the tubular shutter. Each aperture group includes at least a row of holes formed through the wall of the tubular shutter and at least one separate conductor is associated with each hole or aperture in an aperture group for electrical addressing of each hole or aperture in a group separate from the other holes in the group. The tube is rotated so that each aperture group or shutter area sequentially arrives in position for printing or exposing the print-receiving medium with ions. Electrical signals are commutated onto the conductors of the tubular shutter for selectively electrically shuttering the apertures of the aper ture group in printing position for depositing an electrostatic latent dot matrix on the print-receiving medium corresponding to a selected alphanumeric character, image or other symbol. The shutter area is, therefore, effectively scanned in line across the printreceiving medium because of the helical configuration.

In order to prevent ions from passing through other aperture groups in the helix not in the printing position and thereby contaminating the print-receiving medium with extraneous electrostatic charges, a printing slot is interposed between the tubular shutter and printreceiving medium in the form of an ion barrier defining an elongate slot through which the ions pass and so'that successive aperture groups in the helix formed on the tubular shutter are brought in sequential alignment with the printing slot during rotation. The shutter area through which printing is intended at any particular time is sequentially transposed along the printing slot and across the print-receiving medium. A clocking arrangement is, of course, provided for synchronizing the aperture positions and the commutated electrical signals. By this unique construction and arrangement and combination of electrical and mechanical shuttering or modulation, the electrical control apparatus is considerably simplified over conventional electrostatic printing equipment. Thus, the number of electrical circuits, electrical drivers, switches and commutators can be significantly reduced. With reference to the tubular shutter arrangement, only one aperture group is in printing position at any particular time although a plurality of aperture groups or shutter areas are provided in the helix around the tube. Thus, a single conductor can be associated with one hole in each aperture group, row or matrix in the form of a printed metal trace, wire or several wires. Thus, if each aperture group consists of five apertures or holes, a total of five conductors separately electrically addressed and five associated electrical circuits, drivers and commutators is all that would be required for addressing all of the holes of all of the aperture groups of the tubular printing head. While application of an electrical signal to one of the conductors addresses a single hole in every one of the aperture groups around the helix, only one is in printing position, namely the shutter area aligned with the printing slot, while ions passing through any other of the aperture groups are mechanically blocked. High speed electrical switching of the signals applied to the five conductors during rotation of the tubular shutter or printing head thus permits high speed character serial and line serial printing as each shutter area is scanned into position across the print-receiving medium.

ln a preferred form of the invention, the shutter area comprises apertures or holes across or through each of which a pair of electrical potentials is applied to provide double-layered charge or bipolar electrical control over the aperture. In the example of the tubular shutter, the entire inner surface of the shutter may be coated with a layer of conductive material so that a potential can generally be applied or maintained on one side of each of the holes or apertures comprising each of the aperture groups arranged in the helix around the tube. Around the outside of each tube are formed separate conductors for separately electrically addressing, i.e., applying separate electrical potentials to each of the holes within an aperture group. These separate conductors may, for example, be in the form of printed metal traces or one or more wires so that a separate electrical potential can be applied at the outside of each of the holes. A feature and advantage of this arrangement is that fringing lines of force or electrical fields can be formed and established within the apertures or holes of an aperture group between the metal layers or conductors formed on either side of each hole for precise control of ions or other charged particles directed through the apertures. The orientations and strengths of each of the fields within the apertures can be controlled by separate electrical addressing to enhance the flow of ions or other charged particles through the holes, block the flow of ions or other charged particles through the holes and control the density of flow through the hole over a continuous range in between blocking and enhancing. Thus, the tight electrical control permitted by associating a conductive layer or conductor on either side of each aperture or hole in an aperture group permits continuous electrical shuttering control, i.e., 100 percent greyscale control over each of the apertures.

According to another aspect of the invention, the printing or exposure of any particular alphanumeric character in the form of an electrostatic latent dot matrix on the print-receiving medium is itself accomplished serially or sequentially. Thus, in one form the aperture group or shutter area consists of a row of holes or apertures or two rows of offset holes or apertures to provide complete coverage of the print-receiving medium. As the row of, for example, five holes or apertures is swept across the printing area or printing slot, the electrical signals applied to the holes for selectively modulating the flow of ions through the holes are switched as the row steps through successive positions across the printing slot or printing area. For example, the electrical signals applied to the separate conductors on one side of the holes can be switched seven times as the row of apertures or holes comprising the shutter area are swept across the printing area or printing slot. The result in that case is a five-by-seven dot matrix of dots selectively printed to form the desired alphanumeric character on the print-receiving medium. Upon completion of printing of one dot matrix on the printreceiving medium, the next row of holes in the helix formed around the tubular shutter arrives in position and is swept across the printing area or printing slot while the electrical signals applied to the separate conductors are again switched seven times to form the next alphanumeric character until a complete line is built up in the character serial mode. The next line is then printed by the helix in a line serial mode.

ln order to print a plurality of lines simultaneously on the print-receiving medium, a plurality of helices each comprising successive aperture groups can be formed around the tubular shutter, each helix formed with separate conductors for separately electrically addressing the holes of the aperture groups in the helix.

In another embodiment of the invention, the printing head is constructed andarranged in the form of an apertured belt rather than a tubular or annular cylinder. The belt is interposed between a line ion source such as a corona wire and the print-receiving medium which is transported beneath the belt and aligned corona wire. The belt generally serves to block the passage of ions from the corona wire source to the print-receiving medium except in a shutter area supported by the belt. As heretofore described with reference to the tubular shutter, the shutter area comprises an aperture group or group of holes formed through the belt and having a separate electrical conductor associated with each of the holes for separate electrical addressing. The belt is arranged across the print-receiving medium and is transported in a direction generally transverse to the direction of transport of the print-receiving medium so that the shutter area is transposed to successive printing positions across the print-receiving medium. The angle or orientation between the belt and printreceiving medium can be offset from the perpendicular to compensate for simultaneous motion of the belt and print-receiving medium to provide linear character serial printing across the print-receiving medium. Electri' cal contacts or brushes are provided for applying electrical signals to the separate conductors on one side of the belt for separately electrically addressing each of the holes in the aperture group or shutter area as it is transposed to successive positions across the printreceiving medium.

In this embodiment, the shutter area or aperture group may consist of a column of holes or two columns of offset holes for complete coverage during printing. The column of holes is transported across the printreceiving medium and in any particular printing area is swept across the printing area while the electrical signals applied to the separate holes in the columns are switched. if a column of seven holes is provided by way of example and the electrical signals applied to the holes are switched five times in any printing area, a five-by-seven dot matrix is again provided, the dots in the form of an electrostatic latent dot matrix on the print-receiving medium which is thereafter developed according to known techniques. Successive dot matrices corresponding to desired alphanumeric characters are thereby formed sequentially across the paper or other printing medium. In order to provide simultaneous printing of a plurality of lines, a plurality of belts can be provided for transporting a plurality of shutter areas or aperture groups across the print-receiving me dium, each separately electrically addressed.

As heretofore described with reference to the tubular shutter, in the preferred form the belt is formed with a continuous conductive layer on one side of the belt with separate or segmented conductive elements on the other side of a belt a separate electrical layer or conductor associated with each of the holes of the aperture group for separate electrical addressing while a potential is applied to the continuous conductive layer on the other side of the belt. By this expedient, tight electrical control over the passage of charge particles through the holes can be achieved by means of the fringing lines of force or electrical fields of selectively controlled orientation and strength within the apertures.

It is apparent that the unique combination of electrical and mechanical control techniques envisioned by the present invention can be implemented not only by moving belts and drums but also by discs and other moving elements.

According to yet another aspect of the invention, direct electrostatic printing onto any print-receiving medium, dielectric or otherwise, can be accomplished. In this form of the invention, an ion stream is controlled by means of a printing head of th type and in the manner summarized above. However, instead of directly impinging the ion stream on the print-receiving medium which must then be dielectric in order to support the electrostatic charge, a liquid aerosol or dry toner cloud is introduced in the printing slot or printing area between the printing slot and the print-receiving medium so that selectively moduated and shuttered ion stream impinges upon and selectively charges droplets or particles of the toner cloud which are thereafter accelerated to deposit upon the print-receiving medium in accordance with the dot matrix pattern to be reproduced. In this manner, direct toner printing is accomplished and can be effected upon any printing surface including a conductive surface.

Other objects, features and advantages of the present invention will become apparent in the following specification and accompanying drawings.

FIG. 1 is a diagrammatic perspective view of a moving aperture electrostatic printing system for electrically and mechanically selectively controlling an ion stream.

FIGS. 2a through 2i are diagrammatic side views of the printing steps for printing the electrostatic latent dot matrix of an alphanumeric character using the system of FIG. 1.

FIGS. 3a through 3: illustrate the progressive printing of the alphanumeric character corresponding to the steps of FIG. 2.

FIG. 4 is a fragmentary diagrammatic perspective view of the tubular printing head with shutter areas arranged in a helix.

FIG. 5 is a more complete diagrammatic view of the electrostatic printing system using a tubular or hollow cylindrical printing head carrying aperture shutter areas arranged in the helix.

FIG. Sbis a detailed fragmentary plan view of an alternate two-row arrangement for the apertured shutter areas arranged in a helix around the tubular printing head.

FIG. 50 is a detailed cross-section of an alternative tubular printing head helix in which the apertured shutter areas are arranged along grooves machined in the surface of the tube.

FIG. 5d, is a plan view of the-machined grooves showing the shutter area aperture configuration.

FIG. Se is a detailedside cross-section of a groove of the helix showing a conductive wire, an aperture, and lines of force within the aperture.

FIG. 5f is a detailed end cross-section showing a groove of the helix, a conductive wire positioned in the groove and an aperture with the lines of force extending within the aperture.

FIG. 5g is a detailed fragmentary plan view of yet another tubular printing head helix on a flat surface in which a plurality of conductive wires are associated with each helix of an aperture groove or shutter area.

FIG. 6 is a side cross-sectional view of a tubular or hollow cylindrical printing head electrostatic printing I apparatus while FIG. 6a is a detailed fragmentary side cross-section of the tubular or cylindrical drum printing head showing an aperture shutter area.

FIG. 7 is an end cross-section view of the cylindrical drum printing head and electrostatic printing appara- IUS.

FIG. 8 is a detailed schematic diagram of the electrical control circuitry for the electrostatic printing apparatus of FIGS. 6 and 7.

FIG. 9 is a diagrammatic plan view of an alternative moving aperture electrostatic printing system for character serial and line serial electrostatic printing by mechanical and electrical modulation or shuttering of an ion stream using a moving shutter area.

FIG. 10 is a side cross-sectional view of the alternate electrostatic printing system.

FIG. 11 is a detailed fragmentary plan view of the aperture belt showing a seven aperture column shutter area with a separate electrical conductor for electrically addressing each of the apertures.

FIG. 12 is a diagrammatic perspective view of a moving aperture electrostatic printing system for direct electrostatic printing on any medium.

FIG. 13 is a detailed fragmentary side cross-section of a printing aperture for direct electrostatic printing on any medium.

An example of a system embodying the unique combination of electrical modulation or shutter control over ions moving in an electric field and mechanical motion of the shutter area providing at the same time effective mechanical shuttering is shown diagrammatically in FIG. 1. The ion electrostatic printer 10 is adapted for printing, for example, an alphanumeric, character in a dot matrix in the form of an electrostatic latent dot matrix established on dielectric paper 11 which is thereafter developed according to known techniques as, for example, by toning and fixing. The printing apparatus includes a line corona source 12 which can be, for example, a row of corona point sources or a corona wire as in the specific example of FIG. 1. A line stream of ions originating from the line corona source 12 is accelerated toward the back electrode 13 which may also serve as a support for the dielectric paper or other dielectric print-receiving medium l l. Interposed between the corona source 12 and.

print-receiving medium 11 is a printing slit 14 parallel with the corona source and defined. by a pair of ion barriers 15. Interposed between the corona source 12 and printing slot 14 and, in fact, circumscribing the corona source is a tubular shutter 16 in the form of a tube, drum, or annular cylinder formed of at least an insulative layer and a conductive layer which generally form a barrier to ions originating from the corona source 12.

In the example of FIG. 1, a row 17 of five apertures 18 is formed through the wall of the cylinder or tubularshutter to permit passage of ionsotherwise blocked by as all of the ions are intercepted by the wall of the cylin der. Upon rotation of the cylinder, the row l7of apertures 18 moves into the region of the ion flux or stream accelerated toward the back electrode 13 and also enters the area of printing slit 14 so that ions may pass through the apertures formed in the wall of the tubular shutter and through the printing slit for establishing the electrostatic latent dot matrix on the dielectric paper or other print-receiving medium 11. By electrically addressing each of the apertures of the row by separate electrical signals commutated onto the rotating cylinder, the apertures are electrically turned on or off for electrically shuttering the ion stream. In writing a character or other symbol up to five parallel beams of ions are formed by the five apertures corresponding to the five horizontal dots of, for example, a five-by-seven dot matrix. As the aperture row or shutter area 17 is swept vertically across the area of the print-receiving medium in the printing slot, the selected electrical signals applied separately to the five apertures are switched seven times to form the seven five dot rows of the character or symbol dot matrix deposited on the dielectric paper 1 l. The charge is retained on the dielectric paper or other print-receiving medium forming the electrostatic latent dot matrix which is thereafter developed according to well-known established techniques.

Thus, as the aperture or tubular shutter rotates, the apertures of the shutter area or row 17 move with respect to the paper placing them at successive intervals of time in position to write the successive seven rows or other number of rows of dots required to form the character dot matrix. At the successive intervals of time corresponding to the successive row positions, the apertures are electrically addressed or switched according to selected electrical signals for passing or blocking the ion stream or controlling the ion stream over a continuous range in between, providing effectively infinite grey-scale control as hereinafter more fully described.

The hollow cylinder or tubular shutter 16 which forms the moving element of the electro-mechanical shutter is also referred to herein as the printing head and can assume a variety of configurations.

FIGS. 2a through 2i illustrate diagrammatically the steps in the sequential printing of an alphanumeric character or other symbol, in this example the capital letter A, using the simple apparatus of FIG. 1. As the tubular shutter rotates sweeping the row of apertures across the printing slot, the selected electrical signals applied to each of the apertures is switched at successive intervals of time corresponding in this example to the seven row positions of the five-by-seven dot matrix. At each of the successive seven time intervals corresponding to the seven row positions, the apertures of the row selectively pass or block ions according to the applied signals depositing the electrostatic latent dot matrix in the desired configuration on the printreceiving medium. The results of the printing at each of the steps illustrated in FIGS. 2a through 21' is shown in the corresponding FIGS. 3a through 31'.

In order to achieve character serial printing repeated in a line-by-line fashion as the paper is advanced, the shutter area must be transposed across the paper. This is accomplished in the example illustrated diagrammatically in FIG. 4 by arranging a plurality of shutter areas each in the form of a row of apertures in a helical configuration around the tubular shutter. As heretofore described with reference to FIG. 1, the elongate, hollow cylinder or drum 20 circumscribes a corona wire 21 which provides the line source of ions accelerated in the direction of a back electrode 22 which may serve as the support for a dielectric paper or other printreceiving medium 23. The printing slot 24 parallel with the line ion source 21 and defined by ion barriers 25 is interposed in the ion stream between the tubular shutter 20 and print-receiving medium 23. A plurality of shutter areas 26 through 31, etc. are arranged in a helical configuration around the cylinder 20. Each shutter area is in the form of a row of apertures 32 formed through the cylinder wall and spaced laterally with respect to each other in accordance with the desired spacing between alphanumeric characters or other symbols to be formed on the paper. By selecting a cylinder or tubular shutter 20 long enough to cover an entire printing line and locating each of the aperture rows or shutter areas 26 through 31, etc. at suitable intervals along the helix, the shutter areas will enter the printing slit region 24 successively one after another and viewed through the slit will appear to move laterally across the print-receiving medium until an entire line of characters or other symbols has been established. Thus, the single rotational motion of the drum provides both the vertical scan for establishing and printing each individual character dot matrix and also provides the apparent lateral motion of the shutter area across the paper as required for successive or character serial printing in a horizontal line simulating typewriter action.

The paper is advanced for printing successive lines in the same manner and simultaneous multiple line printing in the character serial mode is possible by providing a number of helices around the tubular shutter in a number equal to the lines to be printed. The shutter areas in each helix are of course separately electrically controlled.

A feature and advantage of the helical arrangement is that while it is possible to'drive each of the holes or apertures formed in the helical row independently, in fact only five electrical drivers or switches are necessary for electrically addressing all of theapertures in the shutter areas arranged in the helical configuration around the tube. Thus, each aperture is electrically connected to a corresponding aperture in each of the shutter areas. While each of the apertures in a particular shutter area is separately electrically addressable, all of the shutter areas are thereby addressed simultaneously. Only one of the shutter areas, however, is in the printing position over printing slot 24 at any particular time.

A variety of tubular shutter structures for accomplishing separate electrical addressing of the apertures in a particular shutter area while simultaneously addressing all of the shutter areas are illustrated by way of example in FIGS. 5a through 5g. By these arrangements, a considerable simplification in the electrical circuitry and structure over conventional electrostatic matrix head printers is achieved. As shown in FIG. 5, the moving printing head is a tubular shutter 40 of the type illustrated in FIG. 4 formed of a central insulating layer 41 of plastic tubing or similar material coated on its inner surface with a conductive metal layer 42. Around the outside of the tubular shutter 40 are supported the separate or segmented conductors for separately electrically addressing the apertures of shutter areas arranged in the helix 43 around the cylinder. The cylinder 40 is mounted on shaft 44 which forms the axis around which the cylinder is rotated and which also provides the support for a line ion source such as a corona wire mounted within the cylinder. Mounted on the shaft 44 which is fixed to and rotates with the rotating tubular shutter 40 is the electrical signal transfer assembly 45 consisting of, for example, conductive bands operating in association with brushes for commutating electrical signals onto the cylinders. The conductive bands 46 are electrically coupled with the separate conductors arranged around the outside of the cylinder as hereinafter described in detail for separate electrical addressing of the apertures of the shutter areas. Synchronization of the selected electrical addressing signals and the position of the successive shutter areas with reference to a printing slot is accomplished by means of the timing'wheel disc 47 which is fixed for rotation on the shaft 44. The timing disc may utilize, for example, either photo-optical or electrical pick-up for controlling the application of electrical signals to the commutating brush and band assembly according to the position of the cylinder or drum. For example, as each new shutter area, which in the case of FIG. a is a five aperture row, enters the printing region or area of the printing slot, the timing disc 47 provides a timing signal indicating the start of the next character or symbol to be printed and also the end of a particular line. Because the timing wheel or disc assembly 47 is rigidly fixed with respect to the cylinder or drum 40, the drum rotation speed and stability is not critical.

Referring to FIG. 5a, one structural arrangement for the separate conductors formed on the outside of the cylinder or drum 40 is shown. In this example, the drum is formed with a smooth outer surface with five metal strips or traces 48 formed in a helix around the drum coinciding with the helical configuration of the successive shutter areas or aperture groups. Each of the five metal strips or traces printed, deposited or otherwise formed around the plastic tubular support of drum '40. is electrically or insulatively isolated from every other strip. Each of the strips 48 also provides a conductive layer around an aperture in each of the successive shutter areas. In the example of FIG. 50, each of the successive shutter areas comprises a single row of five apertures laterally and vertically displaced from the aperture row on either side. In this geometrical configuration, a single metal strip 48 surrounds and electrically connects the correspondingly positioned hole in each of the aperture rows of shutter areas. Thus, one of the metal strips or traces 48 electrically connects each of the left-most apertures 50 of each aperture row or shutter row. A second strip or trace 48 surrounds and electrically connected the aperture next to the left-most aperture of each aperture row or shutter area, etc.

Another shutter area configuration is illustrated in FIG. 5b. According to this arrangement, each shutter area is formed not by a single row of five holes or apertures but by a pair of rows, one row 51 of two holes and the other row 52 of three holes offset with reference to each other to provide complete coverage during printing. Thus, each of the apertures in the offset rows of two and three holes are separately controlled electrically by metal strips 53 to print a single row of five dots. However, because of the overlap of the printing apertures the formed dots will also overlap to form a solid line.

In the configuration of FIGS. 50 and 5d, a set of, for example, five. grooves 54 are machined in a helical array around the plastic tube 41 coinciding with the helical configuration of the shutter areas. Holes are drilled in the valleys of the grooves at successive intervals around the helix to form the aperture groups or shutter areas. As described with reference to FIGS. 5a and 5b, the holes can be formed in the configuration of a single row of five apertures or in the configuration of a pair of two offset rows.

Referring in more detail to FIGS. 5c and 5d, a conductive wire 55 is seated at the base of each groove 54 so that a wire 55 overlies a hole in each aperture group formed in the grooves 54 for separate electrical addressing of each hole in an aperture group.

As shown in the side eross-section and end crosssection of FIGS. 5e and 5f respectively each of the holes or apertures 58 is formed through the plastic tube 60 which provides the structural support for the tubular or hollow cylindrical printing head. The tube may be formed however of any insulative material. As heretofore described the inside surface of thetube or drum is coated with a layer 61 of conductive material, so that a conductor is formed on either side of each of apertures 58. The metal or other conductive layer 61 constitutes a continuous conductive layer to which a selected fixed potential is supplied thereby establishing a fixed potential at one opening or side of each of the apertures 58. At the outside surface of the drum or hollow cylinder however the conductive wires 55 effectively provide a segmented conductive layer of insulatively isolated segments for establishing separate or different selected potentials at the other opening or side of each of the apertures 58 of an aperture group. The result is that lines of force are established between the conductive wires 55 on one side of the apertures and the continuous conductive layer 61 on the other side.

A critical feature and advantage of this arrangement is that lines of force or fringing fields are established within the apertures for precisely controlling the flow of charged particles directed through the apertures of the shutter area. The strength or magnitude and orientation of the fringing fields established within the apertures is controlled selectively by the signals or potentials applied to the separate conductors 55 which separately address one side of each of the apertures in each of the aperture group and the common potential applied to the continuous conductive layer 61 formed on the inner surface of the tube or cylinder.

Similarly with respect to the embodiment described with reference to FIG. 5a the separate selected electrical potentials are applied to the insulatively isolated metal strips or hands 48 while the common electrical potential is applied to the continuous conductive layer 42 coated on the inner surface of the cylinder. Again by this expedient fringing fields of force are established within the apertures of the aperture group or shutter area of controlled strength or magnitude and orientation according to the applied potentials. In this respect the invention incorporates principles described in US. Pat. Application Ser. No. 864,022 entitled Electrostatic Line Printer, assigned to the common assignee of the present case. The Electrostatic Line Printer invention set forth in that case incorporates a multi-layered particle modulator in one embodiment formed by a layer of insulating material having a continuous layer of conducting material formed on one side of the insulating layer and a segmented layer of conducting material formed on the other side of the insulating layer. At least one row of apertures is provided through the multilayered particle modulator and each aperture is substantially surrounded byor associated with a segment of the segmented layer of conductive material. Each segment of the segmented layer is insulatively isolated from every other segment for separate electrical control and addressing of each of the apertures. By means of the multiple layer configuration, selective potentials applied to the segments of the segmented conductive layer, while a fixed potential is applied to the continuous conductive layer, results in a double layer of charges selectively establishing fringing fields within the apertures of the modulator. The modulator is interposed in an overall applied accelerating electrostatic field which projects charged particles through the row of apertures of the particle modulator. The cross sectional flow density of the particle stream is regulated by the fringing fields which are contained within the apertures and is precisely controlled according to the pattern of potentials applied to the segments of the segmented conductive layer. By this means, enhancing fields, blocking fields and fields of a continuous range of magnitude between blocking and enhancing can be established within the aperture of the modulator for controlling the flow of particles through the apertures over a continuous grey-scale range.

These features of the Electrostatic Line Printer described in that patent application Ser. No. 864,022 are achieved in the moving printing head of the electrostatic printing system of the present invention by the arrangement of conductors on either side of the openings of the apertures of each aperture group, separately electrically addressable on at least one side'for selectively electrically addressing the apertures of each group.

Yet another aperture group construction arrangement for the hollow cylindrical printing head of 55 is illustrated in FIG. g. In this embodiment the tube is formed with a smooth outer surface and a plurality of wires 63 in this case 3 in number are associated with each aperture 64 of an aperture group for more complete electrical control over the outer opening of the aperture 64. In this arrangement the three wires 63 seated on one side of the aperture 64 can be simultaneously addressed by the same potential signal or different potentials can be applied for achieving desired printing effects.

The electro-mechanical apparatus for an electrostatic printer of the type described with reference to FIG. 5 is illustrated in FIGS. 6 through 8. Referring to FIGS. 6 and 7 the tubular or hollow cylindrical printing head is mounted on a base 70 and side support 71 which support the axes 72 and 73 on which the printing drum 74 is mounted for rotation. The axis 72 is fixed to the drum 74 and rotates with the drum within bearings 81 and bearing 82. The axis 73, on the other hand is fixed with reference to the base 70 and side support 71 and the drum 74 rotates relative to the axis 73 around bearings 83. The drum 74 is formed with a hollow cylindrical or tubular side wall 75 through which the printing apertures are formed with the aperture groups or shutter-areas arranged in a helix around the wall 75 of the drum as heretofore described. Mounted inside the drum 74 and the drum wall 75 is the corona wire support mount 77 which is fixed to the stationary axis 73 thereby supporting the corona wire 78 adjacent the wall 75 of the cylinder but at a position stationary relative to the rotating drum. The corona wire mounting structure 77 is supported at its opposite end by the innerend of axis 72 which rotates inside a brushing 84 relative to the corona wire support.

An ion stream originating from corona wire is accelerated in the direction of a back electrode which forms a cover over the paper 85 or other printreceiving medium. Ions of the stream that are selectively passed through apertures in the wall 75 of drum 74 pass through a printing slot 86 to be deposited on the paper or other print-receiving medium 85. Paper is fed across the upper surface of the printing slot between the printing slot 86 and back electrode 80 by means of a rotary solenoid 87 which advances the paper one character line at a time after a complete line has been printing by driving rollers 88.

Electrical addressing of the separate electrical conductive strips or wires formed in the helical configuration around the outer surface of the wall 75 of drum 74 .is accomplished by means of slip rings 90 formed on disc 91 mounted on support 92 which provides the drive pulley for the drum. Thus the disc 91 and drive pulley 92 are fixed to the rotating shaft 72 for rotation with the drum. Electrical signals are applied to the rings 90 of the disc 91 by means of brushes 93. As shown in FIG. 6 the set of brushes 93 includes four brushes which maintain electrical contact with four of the seven slip rings of disc 91. A second set of brushes containing three brushes for maintaining electrical contact with the other three slip rings of the set of seven slip rings formed on disc 91 is at a position 90 from the set of brushes 93 and is not visible in the cross-section of FIG. 6 Electrical signals fed through the brushes 93 and slip rings 90 are connected via a set of wires 95 to the set of separate conductors formed along the outer surface of the wall 75 of drum 74, to the continuous conductive layer formed around the inner surface of wall 75 of the drum, and for printing control. Thus, of the seven leads from the slip ring, five provide separate electrical addressing for the five separate conductors either wires or metal strips formed in a helix around the outer wall 75 of the drum 74. In this example each aperture group comprises five apertures separately electrically addressable by the five leads. The sixth electrical lead is electrically connected to the metal layer formed around the inner surface of the wall 75 of drum 74 for applying a selective fixed potential to the inner metal layer. Finally the seventh lead provides a printing control signal hereinafter described.

The control electronics for the printing apparatus of FIGS. 6 and 7 is shown in FIG. 8 and centers around the character generator which generates the five electrical control signals applied to the five separate conductors formed around the outer surface of the drum. The five outputs of character generator 100 control the gates of five transistors 101 which in turn provide the five signal outputs applied through brushes and slip rings to the separate conductors formed around the outer surface of the drum. The five output signals 102 selectively control the magnitude and orientation of the fringing fields within the apertures of an aperture group or shutter area selectively turning the holes on and off and adjusting them over a continuous grey-scale range.

Seven input switches 103 to the character generator 100 control the five aperture control signals, the signal potential applied to the conductive layer of the inner surface of the drum and a seventh printing control signal. The three inputs 104 to character generator 100 provide row control during printing of a particular dot matrix constituting for example an alphanumeric character. Thus, in the case of a five by seven dot matrix, five dots or holes are addressed in seven rows the electrical signals applied to the apertures changing with each of the seven rows of the dot matrix. The inputs 104 provide the row control for printing the seven separate rows of the five by seven dot matrix. The signal on line 105 provides an indication that the particular dot matrix is completed. The row address signals for printing the rows of a particular dot matrix are generated by the divide-by-l6 counters 106 and 107 and associated logic circuitry which provide a count down of clock frequencies generated by the oscillator or clock 108 which is, for example, a multi-vibrator. The timing pulses to initiate character printing originates from photo-electric pick-up 110 via gate 111. This timing pulse also resets the character generator.

Monostable multi-vibrator 112 in association with the signal from photo-electric pick-up 110 provides the reference pulse from gate 111 which indicates a zero point for initiating printing of a character line. Flip-flop 113 provides an indication pulse after one revolution of the drum indicating completion of printing of a charac ter line. A one revolution indicator pulse from flip-flop 113 in turn controls flip-flop 114 alternatively turning the clock 108 and advance paper pulse on and off. Thus, during one revolution or rotation of the drum the clock 108 is on, generating signals for printing a row or line of characters. Flip-flop 114 then shuts off clock 108 and during the second rotation of the drum or cylindrical printing head actuates the advanced paper pulse for advancing the paper or other print-receiving medium one character line during the period of the second rotation. During alternate rotations of the drum a line is printed and the paper advanced as the clock is turned on during one rotation and then turned off during the next rotation while an advanced paper pulse is generated. The advanced paper pulse actuates rotary solenoid 87 which by means of rollers 88 advances the paper 85 or other print-receiving medium one character line.

An alternative structure and arrangement for a moving aperture ion controlled electrostatic printer is illustrated in FIGS. 9 through 11. In this arrangement the moving printing head which provides both electrical and mechanical shuttering of the generated ion streem is in the form of a moving belt 200 arranged for movement and transport across the paper or other printreceiving medium 201. The belt 200 physically blocks the passage of ions originating from corona source 202 travelling in the direction of a back electrode not shown. The corona wire is suspended between two supports 203 and 204 mounted stationary relative to the moving belt and which support the corona wire in a direction parallel and over the elongate belt. The belt 200 is driven by means of motor 205 between rollers or pulleys 206 and 207 by means of gear box 208. The motor 205 also drives a paper strip 210 from a paper supply roll 211 to a developer assembly 212 which may be for example a tower bath assembly which develops the latent electrostatic dot matrices established on the paper or other print-receiving medium.

The belt 200 is formed with a set of apertures or holes therethrough which constitute the aperture group or shutter area which is transported from one side of the tape 201 to the other side between rollers 206 and 207. The roller 206 is driven by motor 205 while roller 207 is mounted as an idler pulley with tension adjustment assembly 213. As shown in FIG. 10 the belt 200 is in the form of an endless belt mounted around the pulleys 206 and 207. A fragmentary segment of the belt is shown in FIG. 11 in which a single aperture group or shutter area 220 is formed through the belt consisting of a column of seven holes 221. The aperture group 220 consisting of a column of seven holes is transported horizontally across the paper as motor 205 drives the endless belt around pulleys 206 and 207 for printing of electrostatic latent dot matrices at successive character positions. The ions are blocked physically from reaching the paper everywhere except at the aperture column group or shutter area 220.

The belt is formed of an insulative strip or carrier 222 coated on the inner surface with a layer 223 of metal or other conductive material. On the outside of the insulative belt layer 222 are formed a plurality of separate conductive strips 224 of metal or other conductive material for separately electrically addressing the apertures 221. Thus, seven conductive strips 224 are provided each insulatively isolated from every other strip and each substantially surrounding one of the apertures 22] of the shutter area.

As heretofore described separate selected electric signals are applied to the conductive strips 224 while a selected fixed potential is applied to the continuous conductive layer 223 on the underside of the belt so that a double layer charge is established at each aperture with one potential at one side or opening of the aperture and another potential established at the other side or opening of the aperture. The potential signals are selected to establish within the apertures fringing fields of force of selected strength or magnitude and orientation for control of ion flow through the apertures.

Electrical signals are applied to the conductive segmented strips 224 by way of an electrical contact pulley 225 which maintains electrical contact with the separate electrically conductive strips formed on the belt 220 as it passes around roller or pulley 206. Thus while motor 205 drives the roller 206, electrical contact pulley 225 in frictional engagement with roller 206 is also driven in turn rotating the slip ring assembly 226 to which suitable electrical brushes are applied. Separate electrical signals for addressing the conductive strips 224 can be derived from an electrical control assembly of the type illustrated in FIG. 8 but with seven outputs from the character generator for application to the seven conductive strips.

During printing of an alphanumeric character or other symbol or image the embodiment of FIGS. 9 through 11 can be operated in a five-by-seven dot matrix mode. Thus, the seven columns would be successively switched and addressed at five column positions for a particular character or symbol as the column is swept through five successive column positions by movement of the belt. Successive five-by-seven dot matrix characters are thereby printed across the printreceiving medium or paper 201 until a full line is completed. The printer can thereby be operated in a character serial and line serial mode.

During printing the belt 200 can be oriented in a direction perpendicular to the paper or printing medium with the paper stepped intermittently for line-by-line printing. However, in the example of FIG. 9 the paper 201 is transported continuously from paper supply roll 211 to the developer assembly 212 while the belt 200 is continuously driven across the paper. Therefore the belt is oriented at an angle with respect to the paper to compensate for paper motion and continuous character serial and line serial printing is achieved.

Additionally a plurality of aperture groups can be provided on a single belt or a plurality of belts can be provided for printing more than one line and more than one section of a line at a time. 7

It is apparent that other moving printing head configurations can be constructed to embody the moving printing head for both electrical and mechanical shuttering of an ion stream such as a variety of drum, disc, and belt arrangements. Thus, yet another embodiment the line ion source is arranged in the configuration of a circle and the movable aperture printing head comprises a disc carrying a shutter area in the form of a row or column of apertures formed through the disc. The disc is interposed between a line ion source which is arranged in a circle and a print-receiving medium to block the stream of ions originating from the ion source except in the shutter area. Separate electrical conductors are provided on the surface of the disc for separately electrically addressing the apertures of the shutter area in turn selectively to control the passage of ions through the aperture area. The aperture area is transposed in a circular mode by rotation of the disc for printing the sequential positions of the print-receiving medium.

A moving aperture electrostatic printing system for printing on any surface or print-receiving medium including conductive materials is illustrated in FIGS. 12 and 13. In the embodiment illustrated therein the moving printing head consists of a rotating tubular cylinder or drum 300 of the type heretofore described. A rotataing drum or cylinder is formed by a central insulative layer 301 which may be for example a plastic tubing coated on its inner surface by a continuous conductive layer 302 of metal or other conductive material. An array of aperture groups forming the shutter areas is arranged in a helical configuration around the tube with a segmented conductive layer 303 formed by separate metal strips or wires formed on the outer surface of the tube for separately electrically addressing each of the holes or apertures of each aperture group. A corona wire source 304 suspended within the tubular printing head 300 provides a stream of ions directed toward back electrode 305 and the print receiving medium 306 which may be made of any material suitable for receiving toner particles including both conductive and dielectric material. Instead of a single printing slot interposed between the printing head 300 and printreceiving medium 306 as in the embodiment heretofore described, a pair of printing slots formed by a first pair of barriers 307 and a second pair of barriers 308 is interposed in the ion stream path between the printing head 300 and print-receiving medium 306. The two pairs of barriers 307 and 308 define a channel or passageway 310 through which toner particles are delivered in the direction of arrow 3] I.

As shown in more detail in FIG. 13 uncharged toner particles 312 generated by a suitable toner source 313 are transferred through the channel 310 and across the printing slot formed by the two pairs of barriers 307 and 308 to encounter a stream of ions 313 originating from corona wire 304 and accelerated in the direction of back electrode 305. The toner particles 312 may be in the form of dry toner particles or liquid aerosol droplets and the toner source 313 provides a cloud which is carried by a suitable air pressure differential through the channel 310 and across the printing slot and stream of ions 313.

The stream of ions 313 is intercepted by the wall of the tubular printing head 300 and is thereby blocked except in the location of apertures 314 of an aperture group which have been separately electrically addressed along the separate conductive strips or wires 303 to permit passage of ions 313 through the apertures 314. The fringing electrical fields of force within the apertures 314 extending between conductive layers 302 and 303 can be established at selected orientations and strengths according to the potential applied to the conductive layer 302 and according to the selected potentials applied to the separate conductive strips or wires 303 addressing the apertures 314.

Ions 313 selectively passed through particular apertures 314 in an aperture group encounter and impinge upon the uncharged toner particles 312 delivered through channel 310 selectively charging the particles which are thereafter accelerated toward the back electrode 305 depositing upon the print-receiving medium 306 for direct toner marking printing. Thus, the initially uncharged toner particles 312 delivered between the printing head 300 and print-receiving medium 306 are selectively charged by the selectively passed ion stream to be accelerated and deposited upon the print receiving medium 306 in accordance with the pattern or image to be reproduced. The deposited toner marking particles can thereafter be fixed according to known techniques.

Other arrangements and configurations of system for direct toner marking on any material applicable in the present invention are set forth in United States Patent Application Ser. No. l0l,68l entitled Electrostatic Printing System and Method Using Ions and Toner Particles, assigned to the assignee of the present case.

What we claim is:

1. An electrostatic printer comprising:

means for transporting a print receiving medium;

means for generating a line source of ions in the direction of said printreceiving medium;

means for blocking the ion stream, for providing a shutter area for selectively exposing the printreceiving medium, and for sequentially scanning the shutter area in a direction across the printreceiving medium comprising a tubular shutter of solid material surrounding the line source of ions and having a plurality of aperture groups arranged in a helix around said tubular shutter, each aperture group comprising at least a row of holes formed through the wall of the tubular shutter, each hole in a row having at least one conductive element associated with said hole separate from the conductive element associated with each other hole in the row;

means for rotating said tubular shutter;

means for selectively electrically shuttering the apertures in each row comprising means for commutating'electrical signals on to the conductors associated with apertures in said tubular shutter;

and a printing slot interposed between the tubular shutter and print receiving medium comprising an ion barrier defining an elongate slot whereby suceessive aperture groups in the helix formed on said tubular shutter are brought in sequential alignment with said printing slot during rotation of the tubular shutter so that a shutter area is sequentially transposed along the printing slot and across the printreceiving medium.

2. An electrostatic "printer set forth in claim 1 wherein said tubular shutter comprises a cylindrical tube of non-conductive material having coated over the inner surface thereof a continuous layer of conductive material, and having formed on the outer surface thereof a plurality of conductive elements at least one conductive element associated with each hole of an aperture group.

3. An electrostatic printer comprising:

means for transporting a print receiving medium;

means for generating a line source of ions in the direction of said print-receiving medium;

means for blocking the ion stream, for providing a shutter area for selectively exposing the printreceiving medium, and for sequentially scanning the shutter area in a direction across the print receiving medium comprising a belt aligned between the line source of ions and the printreceiving medium said belt formed with a shutter area of a group of apertures comprising at least a column of holes formed through the belt each hole in the column having at least one conductive elem'ent associated with said hole separate from the conductive element associated with each other hole in said column;

means for transporting said belt across the printreceiving medium;

and means for selectively electrically shuttering the apertures in the column formed through said belt comprising means for commutating electrical signals onto the conducting elements associated with the apertures in said belt.

4. A method of electrostatic printing comprising:

supporting and transporting a print-receiving medium;

directing a line stream of ions toward the printreceiving medium;

interposing a printing slot in the stream of ions;

blocking the line stream of ions in the printing slot with an ion barrier;

providing a shutter area of a row of electrical addressable apertures in the line stream of ions;

selectively applying electrical signals to the electrically addressable apertures of the shutter area selectively and electrically to shutter ions directed through the printing slot;

sweeping the row of apertures across the printing slot while switching the electrical signals applied to the apertures;

and transposing the shutter area sequentially along the printing slot for selectively exposing the printreceiving medium to ions at sequential positions across the print-receiving medium.

5. An electrostatic printer comprising:

a tubular printing head formed with a plurality of aperture groups arranged in the configuration of a helix around said tubular printing head, each aperture group comprising a shutter area, at least one conductor associated with each aperture, said apertures formed through the wall of said tubular printing head;

means for supporting and transporting a print receiving medium past a position adjacent said tubular printing head;

back electrode means located on one side of the print receiving medium position opposite said tubular printing head;

a line source of ions arranged within said tubular printing head for directing an ion stream toward the back electrode means;

means for rotating said tubular printing head;

ion barrier means defining a printing slot interposed between said tubular printing head and said print receiving medium position whereby, upon rotation of said tubular printing head, the shutter area is effectively transposed across the printing slot and print receiving medium position while each aperture group is swept across the printing slot in a direction generally orthogonal to the direction of the transposition of the shutter area;

means for selectively applying electrical signals to the conductors associated with said apertures to electrically selectively shutter ions through said apertures in the shutter area;

means for synchronizing the shutter area position and said electrical signals.

6. An electrostatic printer comprising:

means for supporting and transporting a print receiving medium past a position;

back electrode means located on one side of said print receiving medium position;

a line source of ions arranged along the other side of said print receiving medium position for directing an ion stream toward the back electrode means;

belt means for blocking the ion stream originating at said line source of ions, for providing a shutter area for selectively passing ions from the ion stream, and for transposing the shutter areas sequentially along said line source of ions, said shutter area comprising a plurality of said apertures formed through said belt means, said shutter area inter posed between said line source of ions and said print receiving medium position, said belt means comprising a layer of non-conductive material having coated on one side thereof a continuous layer of conductible material, and having formed on the other side thereof a plurality of conductive elements, at least one conductive element associated with each hole of the aperture group;

means for sweeping said shutter area in a direction generally orthogonal to the direction of transposition of said shutter area;

means for applying electrical signals to the holes of said shutter area and for switching said electrical signals during the sweeping of the aperture group orthogonally to the direction of transposition of the shutter area to electrically selectively shutter ions through said apertures in the shutter area; and

means for synchronizing the shutter area position and said electrical signals.

7. An electrostatic printer as set forth in claim 6 wherein is provided means for switching the electrical signals supplied to the separate conductive elements of each aperture of an aperture group during rotation of said aperture group across a printing slot whereby a latent electrostatic dot matrix is formed on said printreeeiving medium by each aperture group.